Women who have been treated for early signs of cervical cancer have a high risk of the disease decades later, say Swedish researchers.

Regular smear tests should be offered to those with pre-cancerous lesions for at least 25 years, they said.

Current guidelines for UK women who have been treated for the condition called carcinoma-in-situ recommend annual screening for 10 years.

The study of 133,000 women is published in the British Medical Journal.

Cervical screening is offered to women in the UK at three-year intervals between the ages of 25 and 49 and then every five years until the age of 64 years.

We need to think about whether women will find this reassuring but also up to what age they would be willing to undergo screening

Dr Anne Szarewski, Cancer Research UK

It is done to pick up changes to cells in the surface layer of the cervix which may later develop into cancer.

If abnormal cells are detected they can be monitored, destroyed or removed.

Analysis

Swedish researchers looked at data on women who had been diagnosed with the most severe pre-cancerous lesions - commonly known as carcinoma-in-situ - between 1958 and 2002.

They found the women were more than twice as likely to develop cervical cancer as the general female population and seven times more likely to develop vaginal cancer.

The risk remains for 20 years or more, the results suggest.

They also found that there was an increasing risk of cervical cancer if the woman was older at the time of diagnosis, with a much higher risk for women aged over 50.

Study leader, Dr Bjorn Strander, senior consultant in obstetrics and gynaecology at the University of Gothenburg, Sweden, said: "It must be considered a failure of the medical service when women participate in screening, their pre-cancerous lesions are found and they subject themselves to treatment of those lesions, presumably participate in follow-up programmes, and still develop invasive cancer."

He added that follow-up care had to date been insufficient and women should be offered screening at regular intervals for at least 25 years after treatment.

Dr Anne Szarewski, honorary senior lecturer at the Cancer Research UK Centre for Epidemiology, Mathematics and Statistics in London, said less aggressive treatments for cervical abnormalities had been used in the past 20 years, which may have left women more at risk of developing cancer in the long-term.

But she said that the risk had to be balanced against the huge advantages for most women of avoiding hysterectomy and other treatments which would impair their fertility.

"It should be remembered that the majority of women who are found to have high grade cervical abnormalities are in their 30s and early 40s, a time when they may have not completed - or even started - their family.

She said the issue of longer-term follow-up of these women should certainly be considered.

"We need to think about whether women will find this reassuring but also up to what age they would be willing to undergo screening."